Recently, a blood vessel formation pattern of blood vessels of a body has been attracted as one of unique body characteristics. As a device for imaging the blood vessel formation pattern, an imaging device 1 as shown in FIG. 11 has been proposed, for example.
This imaging device 1 has laser light sources 2 for emitting near-infrared light. On the light path of the near-infrared light emitted from the laser light sources 2, a first filter 3 for allowing light of specific near-infrared light bandwidth out of the near-infrared light to pass therethrough, a second filter 4 for allowing light of near-infrared light bandwidth which is absorbed in hemoglobin in blood vessels, out of light obtained through the first filter 3, and an imaging element 5 are arranged in order.
In this case, the imaging device 1 emits near-infrared light from the light sources 2 in a situation where, for example, a finger FG of a body is inserted between the first filter 3 and the second filter 4, resulting in irradiating the finger FG with the light through the first filter 3. Since this near-infrared light is specifically absorbed in instinct hemoglobin of blood vessel tissues inside the finger FG, scattered light obtained though the finger FG enters the imaging element 5 through the second filter 4 as blood vessel pattern light representing a formation pattern of the blood vessel tissues.
The imaging element 5 performs photoelectric conversion on the blood vessel pattern light with a plurality of photoelectric conversion elements that is arranged in a matrix in correspondence with pixels, in order to treat a signal obtained by the photoelectric conversion elements as a blood vessel image signal.
In this case, the imaging device 1 is provided with a physical shielding unit 7 for covering not only all units 2 to 5 existing on the light path of near-infrared light emitted from the light sources 2 but also the finger FG, so as to eliminates influence of light (hereinafter, referred to as outside light) in the air arriving at the finger FG on the near-infrared light. This, however, arises a large scale problem due to the shielding unit 7.
To solve this problem, such an imaging device has been proposed by the applicant of this invention that irradiates, for example, a finger with irradiation light of a luminance level higher than that of light in the air arriving at a body, performs photoelectric conversion on blood vessel pattern light obtained through the finger, with a solid imaging element, and adjusts imaging sensitivity of the solid imaging element by limiting the amount of the resultant signal per unit time (for example, refer to patent reference 1).
Since this imaging device can relatively reduce the amount of signal being accumulated in the solid imaging element as a result of the photoelectric conversion of the blood vessel pattern light and the outside light arriving at this time, imaging can be performed without physically blocking the irradiation route of the irradiation light and the finger and without substantive influence of the outside light on the imaging sensitivity of the solid imaging element to the blood vessel pattern light.    Patent Reference 1 Japanese Patent Application NO. 2003-371022
The imaging device, however, has a drawback in which an uneven blood vessel image is created because the reflex pathway of near-infrared light varies in a body due to the positions of the light sources and individuals and thus the solid imaging element cannot perform the photoelectric conversion on uniform blood vessel pattern light.